The present invention relates to hydrophobic composites, particulates and free-flowing aggregates, methods of producing same, and applications thereof. More particularly, the present invention relates to hydrophobic composites having a core material coated by a hydrophobic powder having an impure element pre-treated with a hydrophobic hydrocarbon, and optionally with additional coating agents, such that the resulting composites are characterized by superior water-repellency and durability, suitable for various applications. The present invention further related to hydrophobic composites that are prepared in aqueous solutions.
In many applications it is desired to prevent moisture from reaching critical regions using hydrophobic materials which repel water. In the area of civil engineering, when water percolate into construction, salts and minerals present in the water damage the concrete (or other materials from which the construction is made), and causes corrosion and deformation to its reinforcing steel bars or wire fabric. Such corrosion and deformation leads to the appearance of cracks in the concrete and, eventually, to a local reduction of construction strength. Other internal objects, such as pipes, electrical wires, communication channels and the like may also be damage by moisture.
The presence of water in the house is associated with numerous of unpleasant evidences such as, moisture at the base of the walls, under carpeting or under floor tiles; rust at the base of steel posts; stains, discoloration or decay of wood, paneling, drywall and other objects close to the floor, walls or ceiling; molds and mildew on concrete, furnishings or carpets; efflorescence (“white powder”) on the concrete; peeled floor tiles; damp odor; “sweating” walls (condensation of excessive humidity); condensation of water on windows; plugged or damaged rain gutters; growth of moss and the like.
Moisture may percolate into the construction, either vertically, for example because of accumulation of water on roofs or floors of construction/foundations, or horizontally, by leakage of water through external walls of a building for example, because of extreme weather conditions. A sever problem of horizontal leakage is in buried walls or portions thereof, where hydrostatic pressure generated by excess moisture in the surrounding soil pushing in on the outside of the foundation wall, significantly contributes to horizontal leakage.
The percolation of moisture through concrete walls is explained by the porosity of the concrete (about 12%-20%), formed during the curing process when surplus water creates a network of interconnected capillaries, about 10-100 nm in diameter.
As used herein, the term about refers to ±10%.
These capillaries contribute to the percolation of moisture there through via capillary forces. As the concrete ages, the water percolation, gradually leaches out the concrete and makes it more and more porous.
Another problem caused by moisture is mildew, which, apart from being unaesthetic, creates a musty odor. Even though a substantial amount of standing water may be removed by prior art waterproofing methods that utilize a drainage conduit, residual moisture will still cause mildew problems. It is recognized that a prolonged exposure to mildew may cause many health problems, such as, allergies, asthma, skin diseases and the like.
Basement is by far the largest source of moisture in a house. Covered floor and walls in the finished basement trap moisture and eventually cause damp or wet basement. As the pH level of the concrete is high, the alkalis present in the concrete dissolved by the water and attack paints and floor tiles. Hence, even if the basement looks dry, moisture is pouring in by seeping through capillaries. The mildew, which is typically initiated in the basement due to its excessive amount of moisture, may spread to other areas of the house above ground, e.g., by ventilation.
In many countries sand is used as a bed under the floor tiles and is recommended by standards in order to reduce noise. Water, originating from periodic cleaning pluming leakage or heavy rain (e.g., in tiled roofs) generate a substantial amount of excessive weight, up to approximately 100 Kilograms of water per square meter. Large portion of the water is trapped under the tiles and the sand thus remains wet for many years. Such excessive weight is typically taken under consideration by the engineer in the planning stages of the building, which, in order to increase the strength to the construction, uses more concrete and reinforcing material under the sand bed. The contribution of the water and construction extra strengthening to the overall weight accelerates the sinking of the building. The problem is only aggravated in hanging structures such as balconies and overpasses, interconnecting different parts of buildings.
In addition to its excessive weight, the wet sand under the tiles attracts insects, such as ants, warms, aphids, dust mites and the like. Apart from the recognised health problems associated with such attraction, the insects excavate through the sand and accelerate sinking of the tiles.
Being wet most of the time, the sand under the floor tiles becomes a thermal conductor, thus reducing any isolation pretended to be achieved in the design stages of the building. In some buildings, an electrical heating system is constructed under the floor. The contact between these systems and the wet sand may cause a sever damage to the system, or, in extreme cases, even fire may occur.
With respect to under floor waterproofing of balconies or tiled roofs, all prior art methods are directed at positioning a waterproofing material such as a sealing sheet, a bituminous membrane or a solvent based elastomeric coat, under the bed sand supporting the floor tiles. However, almost irrespectively of their quality, the life time of these waterproofing materials is not sufficient, because of the salts containing moisture being present in the sand.
Even in constructions or part of constructions where sand is not in contact with the waterproofing material, the life time of prior art materials is limited. Alkalis dissolved in the water attack paints and adhesives and damage the waterproofing material, by formation of cracks, peels or blisters.
An additional indoors problem related to sealing means is the problem of elevated levels of Radon gas which may be found in houses, typically, but not exclusively, in the lower parts thereof, e.g., basements. Radon is an invisible and odourless radioactive gas, produced by the decay of radioactive heavy metals uranium and thorium, dispersed throughout the Earth's crust. The by-products of the radioactive decay of these metals are lighter radioactive heavy metals which also decay into lighter metals and so on. The decay chain continuously produces radium, which decays into radon isotopes, mainly Radon-222 and Radon-220 (the latter also known as Thoron), where the Radon-222 isotope is the most common indoors radioactive gas.
Radon decay products are tiny radioactive solid particles which float in the air and, breathed by human, get trapped in the lungs, trachea and bronchi. Because of these decay products, the Radon, at the levels common in homes, is about 1,000 times more lethal than the safety limits on any other toxin or carcinogen.
Being the heaviest known gas (nine times heavier than air), the Radon gas naturally moves into the permeable soil and the gravel bed surrounding the foundations of the house and subsequently diffusively penetrates into the house through the above mentioned openings and pores in concrete. Radon is soluble in water and therefore carried to the vicinity of the house by underground streams, and further into the house by the percolation of water, e.g., through the concrete. The most common carrier of Radon into the house is water.
Moisture and water also cause damage to buried objects, such as underground pipes, storage tanks (e.g., gas tanks), tunnels and cables. Due to moisture, corrosion caused by electrolysis, digesting materials, insects and/or micro organisms present in the sand, many buried objects are exposed to damaging processes which reduce the lifetime of the objects. In cases where the buried object contains hazardous materials any leakage there from may have severe environmental consequences.
In the area of electric power industry, numerous research programs have been conducted to identify mechanisms which are responsible for the premature failure of underground electrical or communication cables. It is recognized that many of the premature cable failures are linked to internal build-up of micro sized water branches within imperfections of the insulating layers of the cable, also known as “water trees.” The water filled imperfections branch radially inward through the amorphous insulating materials. As the water progresses radially inward the potential for cable failure increases.
Even when the conducting core of the cable is coated by a sophisticated material such as a liquid crystal polymer, the formation of imperfections is inevitable due to corrosion caused by electrolysis, digesting materials, insects and/or micro organisms present underground.
Buried pipes and electrical or communication channels are often positioned inside hollow underground tubes. The hollow tubes also ease access to the buried object, for maintenance purposes. However, water or other liquids occasionally find the way into the space between the buried object and the internal surface of the surrounding tube (e.g., through holes or cracks formed in the external surfaces of the tubes, or through the gap between contacting tubes). The water flows through the tube and causes damages to the buried objects or to connection boxes at the end of the tube.
The combination of moisture and sand tends to harden or freeze. The formed hard material is known to transform axial stresses from the surrounding environment to the buried object. When the level of the axial stresses exceeds the object's characteristic strength, the object is damaged. To prevent the above axial stresses, the objects are made stronger and/or being buried deep into the ground. It is recognized, however, that the cost of positioning objects underground increases with the depth in which these objects are to be buried. Moreover, deep buried objects are difficult to be accessed, e.g., for maintenance or replacement.
One way to protect an underground object tube is by applying a sealing coat on the object or its surrounding tube, so as to prevent the above agents from damaging its external surface. However, although in general such coats survive the attack of digesting materials or organisms, very often local damages to the coat are inevitable (for example due to axial stresses), which local damages are sufficient to initiate the erosion of the object.
Generally, moisture can be prevented from reaching critical regions by the use of hydrophobic materials which repel water. Design considerations for hydrophobic materials depend on the application for which such materials are designated, and include water intrusion pressure, thickness, chemical compatibility, airflow, temperature compatibility and the like. Water intrusion pressure is a measure of a critical pressure under which water are forced through the hydrophobic material. Chemical compatibility is important in applications where the hydrophobic material comes in contact with corrosive material.
Another structure for which waterproofing is required is a water reservoir, where the base and the walls thereof need to be impermeable so as to prevent water from leaking out. The problem of leaking reservoir is crucial in arid regions where one desire to maintain the content of the reservoir for as much as time possible.
A typical reservoir is a flat area surrounded by a sloping embankment. In many prior art waterproofing methods, the bottom of the reservoir (both the flat base and the sloping embankment) are covered with sealing sheets (typically made of high density polyethylene, HDPE), adhered or welded to each other. This method suffers from many drawbacks. First, because the waterproofing is by a plurality of bonded sealing sheets, there are many areas near the connection between two adjacent sheets where the bonding is damaged or not perfect, and the sheets become permeable. Second, due to its limited elasticity, the sealing sheet tends to be damaged by hard objects, being in contact therewith either from above or from below. Third, during maintenance, when the bottom of the reservoir is cleaned by light machinery or manually, the sealing sheets may be ruptured. Forth, forces induce earth movements or cracks formation (e.g., in a man made concrete reservoir) rupture the sealing sheets. An additional limitation of prior art method is originated by colonies of insects and organisms present under the sealing sheets. In which case purification chemicals are required to purify the content of the reservoir.
Waterproofing is often required also in agriculture or gardening where irrigation is employed. When an area is artificially irrigated by water, only a relatively small portion of water reach the plants growing on the soil. Most of the water seeps through the earth or evaporates. The need to save water is also related to other agricultural problems, such as salty soil and underground salty water. Generally, when designing an area for gardening or for industrial agriculture use, it is difficult to provide the plant a sufficient amount of water without causing rottenness, while, at the same time, preventing hazardous materials (such as salts) from damaging the roots.
Design considerations for hydrophobic materials to be used for waterproofing any of the above structures include water intrusion pressure, thickness, chemical compatibility, airflow, temperature compatibility and the like. Water intrusion pressure is a measure of a critical pressure under which water are forced through the hydrophobic material. Chemical compatibility is important in applications where the hydrophobic material comes in contact with corrosive material.
Over the years, numerous hydrophobic materials have been developed, including PTFE, nylon, glass fibers, polyethersulfone and aggregates having hydrophobic properties.
One such material is disclosed in U.S. Pat. No. 3,562,153, to Tully et al. The oil absorbent compositions of the Tully et al. patent are obtained by treating a liquid absorbent material, which may be particulate, granular or fibrous in nature, with a colloidal metal or metalloid oxide which is chemically bonded to an organosilicon compound to render the metal or metalloid oxide hydrophobic. The hydrophobic oxide-treated absorbent composition is contacted with the oil-contaminated water and selectively removes the oil therefrom. The oil absorbent composition of Tully et al. is reported to have excellent water repellency, thus enabling it to maintain its oil absorbent efficiency for long immersion periods.
U.S. Pat. No. 4,474,852, to Craig, which is incorporated by reference as if fully set forth herein, combines ideas of several prior art patents (U.S. Pat. Nos. 3,567,492, 3,672,945, 3,973,510, 3,980,566, 4,148,941 and 4,256,501, the contents of all of which are hereby incorporated by reference). According to Craig, hydrophobic composites having superior water repellency are obtainable by depositing on a particulate and granular core material an adherent first coat which comprises a film-forming polyurethane and asphalt, as an optional additive, and applying to the thus coated core material a second coat comprising a hydrophobic colloidal oxide such as, for example, hydrophobic fumed silica. Craig teaches that the adherent first coat should not exceed 1 weight percentage of the total dry aggregate weight while the second coat is between 0.025 and 0.25 weight percentage of this total weight. Further according to the teachings of Craig, hydrophobic composites prepared in this manner not only prevent water from adhering to the surfaces of the individual composite particles, but also from entering the interstitial spaces of the aggregates of the composites.
WO 03/044124, which is also incorporated by reference as if fully set forth herein, also discloses a method of preparing hydrophobic aggregates, which is based on the teachings of Craig (U.S. Pat. No. 4,474,852). According to the teachings of WO 03/044124, the hydrophobic aggregates disclosed in U.S. Pat. No. 4,474,852 are not satisfactory as they do not withstand water pressure higher than 2-3 centimeters.
In a search for a method of producing hydrophobic aggregates with improved water-repellency and oil absorbency performance and improved durability under higher water pressures, it was concluded, according to the teachings of WO 03/044124, that an improved method of preparing hydrophobic aggregates, as compared with the teachings of Craig, should include changes relating to the compositions of the first and second coat and the relative amounts thereof, to the temperature in the various process steps and to the mixing rate during the course of preparation.
Hence, the method disclosed in WO 03/044124 includes depositing on a particulate or granulate core material an adherent first coat which comprises a film-forming agent such as polyurethane and optionally a gluing agent such as liquid asphalt, and applying to the thus coated core material a second coat which comprises a hydrophobic fumed silicate or any other superhydrophobic powder. According to the teachings of WO 03/044124, the adherent first coat constitutes about 1-2 weight percentages of the total dry aggregate weight while the second coat constitutes more than 5 weight percentages of this total weight. Further according to the teachings of WO 03/044124, such hydrophobic aggregate is capable of holding a water pressure of up to 20-30 cm.
Although WO 03/044124 teaches the use of superhydrophobic powders other than hydrophobic fumed silica, this reference neither specifies nor exemplifies such a superhydrophobic powder. This reference also fails to demonstrate any performance of the hydrophobic aggregates disclosed therein with regard to both, water repellency and its behavior under high water pressures. Furthermore, it is well known in the art that using such a large amount of hydrophobic fumed silica as the second coat, as taught by WO 03/044124, reduces the cost-effectiveness as well as the simplicity of the process.
In addition, as hydrophobic fumed silica, as well as other metal oxides treated with organosilicon compounds, such as those disclosed in the Craig patent, are characterized as acidic substances, aggregates coated by such materials are susceptible to reactions with alkaline reagents such as detergents. This feature limits the use of such aggregates in applications where detergents may be in contact with the hydrophobic aggregates, such as, for example, top-coatings of various surfaces.
U.S. Pat. No. 4,474,852 mentioned hereinabove describes several applications for its hydrophobic composites in waterproofing applications. Mainly as a top coat on paved surfaces, such as asphalt or concrete, a flood coat of asphalt sealer should first be applied over the surface, immediately after which a heavy coat of the hydrophobic composites may be sprayed over and rolled into the asphalt sealer, providing a watertight top coat. The same top coating technique may be used in pothole repairs in roadways.
The composites may also be used as a substitute for common aggregate in asphalt roofing or shingles, or in built-up roofing. In such applications, the hydrophobic composites are effective in preventing water penetration and resulting damage caused by freeze-thaw cycles as well as dimensional changes due to wetting and drying. U.S. Pat. No. 4,474,852 also claims utility as a top coat on paved surfaces, such as asphalt or concrete road surfaces or bridge decking, providing a water-tight finish, which substantially reduces freeze-thaw damage, and which is unaffected by salt compositions normally used for ice removal. In addition, these hydrophobic composites may be applied to painted surfaces to provide a durable, waterproof finish over wood, metal, concrete, stone, brick and certain synthetic substrates. Such hydrophobic composites may also be blended with suitable binding agents to provide a water-repellent coat.
As the American Concrete Institute (ACI) recommends a 3-inch pervious sand bed spread on top of waterproofing sheet under the building, the hydrophobic composite of U.S. Pat. No. 4,474,852 may also be used as a waterproofing agent in pavement construction, as a fill or bed material under concrete slabs or as a gravel fill or ballast for road beds or sidewalks. However, as will be appreciate by a skilled artisan, free-flowing aggregate are made of extremely small particulates hence being easily carried in the wind and washed out by running water. Therefore, without specific and enabling instructions, it would be very difficult and probably not practical to use the hydrophobic aggregate in its flowing form.
Furthermore, presently known methods of producing hydrophobic composites do not result in satisfactory products and are limited by other parameters, such as, for example, cost effectiveness.
There is thus a widely recognized need for, and it would be highly advantageous to have hydrophobic composites, particulates and free-flowing aggregates, methods of producing same and applications thereof, devoid the above limitations.